The invention concerns a method for establishing a sealing connection between the filter mat of a tubular filter element and a metal headpiece which encloses the element on one side in which an annular groove to receive the edge of the filter mat is formed in the headpiece, and the wall of the headpiece, which is adjacent to the circumference, is pressed from the circumference of the headpiece inwards so as to reduce the inside diameter of the annular groove by applying pressure, which is directed radially toward the inside.
Known methods of this type are preferably used with filter elements, which are provided for the filtering of media which are hard to control and where filter mats made of stainless steel are used. The media which can be taken into consideration for such filter elements are highly viscous and/or aggressive fluids with temperatures which are often very high, for example, polymer melts which are filtered, so as to be supplied to spinning nozzles to establish a textile starting material.
Although the known methods of the type mentioned in the beginning make possible the establishing of a satisfactory sealing connection between the filter mat and the headpiece, the pressing of the outer wall of the groove formed in the headpiece with the filter mat, however, leads to a constriction of the pertinent circumference area of the filter element. This area of reduced diameter forms a dead space in the circumference area of the filter element, in which the medium to be filtered accumulates, wherein in the case of highly viscous and/or melted media, there is a thermal degradation of the material. This leads to operating disturbances and operating interruptions and to quality losses in the product.
The goal of the invention is to indicate a method, which makes possible the establishing of a satisfactory sealing connection and also ensures improved operating characteristics of the pertinent filter element.
With a method of the type mentioned in the beginning, this goal is attained, in accordance with the invention, in that the wall of the annular ring, which is adjacent to the circumference, is provided with a thickening that increases the diameter of the headpiece and that pressure is applied for the compression in the area of this thickening.
This makes it possible to prevent the compression in the circumference area of the headpiece from leading to a constriction in the pertinent circumference area of the headpiece, because the xe2x80x9cexcessxe2x80x9d material volume, which is made available by the wall thickening, prevents the formation of the constriction produced in the known method during the flowing process caused by the compression, in that it fills the otherwise formed dead space.
Advantageously, the headpiece is provided with such an annular groove, which has a larger inside diameter on the base of the groove than in the area further away from the base of the groove, and the thickening is formed at a distance from the base of the groove. With such a shaping, the nonthickened wall area forms a kind of bending joint on the circumference of the headpiece, by means of which the thickened wall area of the annular groove is joined together with the rest of the headpiece, so that even with a relatively voluminously shaped thickening, a shaping of the thickening, inwards and in the desired manner, is facilitated during compression as a result of the nonthickened wall area, which forms a bending joint.
An increase of the outside diameter of the headpiece, which perhaps remains after the compression and which is formed by the thickening, can again be eliminated, after the compression, by mechanical processing, in which the circumference of the headpiece is abraded to the theoretical diameter. Preferably, the abrasion is carrying out by machining the area of the thickening. The filter element can be shaped in its outer contour in this manner so that the circumference of the headpiece is joined, in an aligned manner, with the protective basket, which covers the filter mat on its outer side, without a substantial gap forming a clearance space.
The object of the invention is also a filter element, which is produced in accordance with the method of the invention and which has the features of claim 6.